We hypothesize that a subset of human mutations in PKD1 and PKD2 result in protein products whose main pathologic defect is improper folding resulting in failure of trafficking into the cilial compartment. This proposal seeks to define critical determinants of polycystin trafficking and to explore the role these have in the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD). We will determine the role of polycystin-1 trafficking in the pathogenesis of ADPKD. The underlying hypotheses of this aim is that a subset of pathogenic amino acid substitution mutations result in aberrant trafficking of PC-1. We will define the role of specific domains and mutations in the localization of PC-1 in the cilia in epithelial cells by examining the consequences of amino acid substitution mutations and cleavage at the GPS site on trafficking of PC-1 to cilia. We will determine the role of the cytosolic C-terminus in the trafficking of full length PC-1. In the second aim, we will identify the determinants of polcysytin-2 trafficking to cilia. We have found that PC-2 contains independent cilia targeting information within its primary sequence that is both necessary and sufficient for cilia targeting. We will use discovery of the responsible motif(s) to elucidate the mechanism by which this and other PKD-related proteins achieve cilial location. Our goal is to identify the necessary and sufficient amino acid motif(s) in PC-2 that direct its localization to cilia. We will isolate proteins interacting with the PC-2 trafficking domain that are part of its ciliary trafficking complex. Finally, we will determine the role of protein trafficking in the clinical features of ADPKD. We will test the hypothesis that disruption of trafficking is a true pathogenic event in ADPKD and that trafficking mutations result in milder clinical features than complete null mutations. We will determine whether naturally occurring disease causing amino acid substitution mutations in PC-2 result in defective trafficking of the protein. We will investigate whether trafficking mutations result in hypomorphic alleles with milder cyst forming capacity than null alleles in true in vivo models due to Pkd1 and Pkd2. This aim will establish in vivo model systems for determining the clinical impact of trafficking mutants and for determining whether therapies directed at trafficking of PC-1 and PC-2 will be effective in the treatment of patients.